Conventionally, there has been known a pump where a pair of pressing elements are rotated so as to press a tube thus displacing a liquid from one end side to the other end side of the tube (for example, see Japanese Unexamined Patent Application, Publication No. Hei5-263765 (hereinafter referred to as PTL 1)).
In the pump disclosed in PTL 1, a rotary shaft to which one pressing element is connected is projected upward, and a rotary shaft to which the other pressing element is connected is projected downward. The pump disclosed in PTL 1 is configured such that drive forces of a pair of electric motors are respectively transmitted to the rotary shafts, which project upward and downward, through a pair of reducers so that the pair of pressing elements are rotated at non-constant velocities thus displacing the liquid by small pulsation.
The pump disclosed in PTL 1 includes a drum having an arcuate inner peripheral surface and a tube disposed on the inner peripheral surface of the drum. The pump is configured such that the rotary shafts connected to the pair of pressing elements and a drive mechanism for driving the rotary shafts project upward and downward from the drum.